Traveling control method and traveling control device for vehicle

ABSTRACT

A travel control method for a vehicle includes: presenting a vehicle traveling on a route to a preliminarily set destination with overtaking information as to whether to accept execution of an overtaking assist function for overtaking a preceding vehicle by changing lanes through autonomous travel control; and executing the overtaking assist function when an acceptance input of accepting the execution of the overtaking assist function is detected in response to presentation of the overtaking information. This method further includes: detecting a position of the vehicle on the route; and detecting whether or not there is a traveling direction change point on the route ahead of the position of the vehicle, a point at which the vehicle must change its traveling direction. When the distance from the vehicle to the traveling direction change point is shorter than a preliminarily set distance, the presentation of the overtaking information is not performed.

TECHNICAL FIELD

The present invention relates to a travel control method and a travelcontrol apparatus for a vehicle that include autonomous travel control.

BACKGROUND

An automated (autonomous) driving system equipped in a vehicle is known,which is configured to propose a lane change to a next lane to thedriver. In the automated driving system described in JP2018-025989A, forexample, when the density of vehicles in a next lane to the travelinglane is lower than a threshold density, a lane change to the next laneis proposed to the driver.

SUMMARY

According to the above prior art, however, in the vicinity of abranching point or merging point on a route to a preliminarily setdestination, a lane change may be proposed to the vehicle which istraveling on the route. For example, when a lane change is performednear a branching point or the like in accordance with the proposal andthe branching point or the like is located in the lane before the lanechange, it may not be possible to return to the lane including thebranching point or the like depending on the road congestion or thelike.

A problem to be solved by the present invention is to provide a travelcontrol method and a travel control apparatus for a vehicle with which,for a vehicle traveling along a route to a preliminarily setdestination, proposal of a lane change is not performed at the timingwhen the traveling along the route is hindered.

In the present invention, a vehicle traveling on a route to apreliminarily set destination is presented with overtaking informationas to whether or not to accept execution of an overtaking assistfunction for overtaking a preceding vehicle by changing lanes throughautonomous travel control. The above problem is solved by not performingthe presentation of the overtaking information when a distance from thevehicle to a traveling direction change point is shorter than apreliminarily set presentation prohibition distance.

According to the present invention, the presentation prohibitiondistance is appropriately set and the overtaking information can therebybe prohibited from being presented at the timing when the travelingalong the route is hindered. This can prevent the driver frominadvertently accepting the overtaking information near the travelingdirection change point such as a branching point so as not to be able toreturn to the lane including the traveling direction change point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of the travelcontrol apparatus for a vehicle according to the present invention;

FIG. 2 is a front view illustrating a part of the input device of FIG.1;

FIG. 3 is a plan view illustrating automated (autonomous) lane changecontrol using a lane change assist function;

FIG. 4 is a plan view illustrating automated (autonomous) lane changecontrol to an adjacent lane using an overtaking assist function;

FIG. 5 is a plan view illustrating automated (autonomous) lane changecontrol to the original travel lane using the lane change assistfunction;

FIG. 6 is a plan view illustrating automated (autonomous) lane changecontrol using a route traveling assist function;

FIG. 7 is a block diagram illustrating a state transition of the controldevice of FIG. 1;

FIG. 8 is a flowchart illustrating a basic travel control process of thetravel control apparatus for a vehicle according to the presentinvention;

FIG. 9 is a plan view illustrating a technical problem caused by thebasic travel control process of the travel control apparatus for avehicle according to the present invention;

FIG. 10 is a plan view illustrating a first embodiment in which apresentation prohibition distance is set in order to solve the technicalproblem illustrated in FIG. 9;

FIG. 11 is a flowchart illustrating a travel control process of thetravel control apparatus for a vehicle according to the firstembodiment; and

FIG. 12 is a flowchart illustrating a procedure for setting thepresentation prohibition distance in accordance with the presence orabsence of route setting or the like in a second embodiment.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating the configuration of a travelcontrol apparatus 1 for a vehicle (also referred to as a “subjectvehicle,” hereinafter) according to an embodiment of the presentinvention. The travel control apparatus 1 for a vehicle according to thepresent embodiment represents an embodiment for carrying out the travelcontrol method for a vehicle according to the present invention. Asillustrated in FIG. 1, the travel control apparatus 1 for a vehicleaccording to the present embodiment includes sensors 11, a subjectvehicle position detection device 12, a map database 13, onboardequipment 14, a navigation device 15, a presentation device 16, an inputdevice 17, a drive control device 18, and a control device 19. Thesedevices are connected to one another, for example, via a controller areanetwork (CAN) or other onboard LAN for mutually exchanging information.

The sensors 11 detect a traveling state of the subject vehicle. Thesensors 11 include, for example, cameras such as a front camera thatcaptures images ahead of the subject vehicle, a rear camera thatcaptures images behind the subject vehicle, and side cameras thatcapture images on the right and left sides of the subject vehicle.Additionally or alternatively, the sensors 11 include radar devices suchas a front radar that detects obstacles ahead of the subject vehicle, arear radar that detects obstacles behind the subject vehicle, and sideradars that detect obstacles existing on the right and left sides of thesubject vehicle. Additionally or alternatively, the sensors 11 include avehicle speed sensor that detects the vehicle speed of the subjectvehicle, a touch sensor (capacitance sensor) that detects the holding ofthe steering wheel by the driver, a driver monitor that captures imagesof the driver, etc. The sensors 11 may be represented by one of theabove-described various sensors or may also be configured as acombination of two or more sensors. The detection results of the sensors11 are output to the control device 19 at predetermined time intervals.

The subject vehicle position detection device 12 includes a GPS unit, agyro-sensor, a vehicle speed sensor, etc. The subject vehicle positiondetection device 12 detects radio waves transmitted from a plurality ofcommunication satellites using the GPS unit to periodically acquire thepositional information of a target vehicle (subject vehicle). Inaddition, the subject vehicle position detection device 12 detects thecurrent position of the target vehicle based on the acquired positionalinformation of the target vehicle, angle variation information acquiredfrom the gyro-sensor, and the vehicle speed acquired from the vehiclespeed sensor. The subject vehicle position detection device 12 outputsthe detected positional information of the target vehicle to the controldevice 19 at predetermined time intervals.

The map database 13 is a memory that stores three-dimensionalhigh-precision map information including positional information ofvarious facilities and specific points and is accessible from thecontrol device 19. The three-dimensional high-precision map informationis three-dimensional map information based on the road shape detectedwhen traveling on an actual road using a vehicle for data acquisition.The three-dimensional high-precision map information is map informationin which detailed and highly precise positional information items, suchas a curved road and the size of the curve (e.g., curvature or radius ofcurvature), a merging point and a branching point of a road, a tollgate,and a position at which the number of lanes is reduced, are associatedwith the map information as the three-dimensional information.

The onboard equipment 14 includes various modules equipped in thevehicle and is operated by the driver. Examples of such onboardequipment include a steering wheel, an accelerator pedal, a brake pedal,direction indicators, wipers, lights, a horn, and other specificswitches. When the driver operates the onboard equipment 14, itsoperation information is output to the control device 19.

The navigation device 15 acquires the current positional information ofthe subject vehicle from the subject vehicle position detection device12 and superimposes the position of the subject vehicle on the mapinformation for navigation to display the position of the subjectvehicle and the map information on a display or the like. In addition,the navigation device 15 has a navigation function of setting a route toa destination and guiding the set route to the driver when thedestination is set. This navigation function serves to display the routeon the map of the display and inform the driver of the route by voice orthe like. The route set by the navigation device 15 is also used in aroute traveling assist function of the control device 19. The routetraveling assist function is a function used for controlling the subjectvehicle to autonomously travel to the destination based on the setroute.

The presentation device 16 includes, for example, one or more displayssuch as a display of the navigation device 15, a display incorporated ina rearview mirror, a display incorporated in a meter unit, and a head-updisplay projected on a windshield. Additionally or alternatively, thepresentation device 16 includes one or more devices other than thedisplays, such as a speaker of an audio device and a seat device withembedded vibrating bodies. The presentation device 16 informs the driverof various presentation information items under the control by thecontrol device 19.

The input device 17 is, for example, a device such as a button switch ora touch panel disposed on a display screen with which the driver caninput information by the manual operation or a microphone with which thedriver can input information by the voice. In the present embodiment,the driver can operate the input device 17 thereby to input settinginformation in response to the presentation information which ispresented by the presentation device 16. FIG. 2 is a front viewillustrating a part of the input device 17 of the present embodiment andrepresents an example including a set of button switches arranged on aspoke part or the like of the steering wheel. The illustrated inputdevice 17 is a button switch used when setting ON/OFF or the like of theautonomous travel control function (autonomous speed control functionand autonomous steering control function) of the control device 19. Theinput device 17 includes a main switch (MAIN SW) 171, aresume/acceleration switch (RES +) 172, a set/coast switch (SET −) 173,a cancel switch (CANCEL) 174, an inter-vehicle distance adjustmentswitch (DISTANCE) 175, and a lane change assist switch (L/C) 176.

The main switch 171 is a switch for turning ON/OFF the power source ofthe system which achieves the autonomous speed control function andautonomous steering control function of the control device 19. Theresume/acceleration switch 172 is a switch for turning OFF the operationof the autonomous speed control function and then resuming theautonomous speed control function at the set speed before the OFF state,for increasing the set speed, and/or for following a preceding vehicleto stop and then restarting. The set/coast switch 173 is a switch forstarting the autonomous speed control function at the speed whentraveling and/or lowering the set speed. The cancel switch 174 is aswitch for turning OFF the autonomous speed control function. Theinter-vehicle distance adjustment switch 175 is a switch for setting theinter-vehicle distance from a preceding vehicle and is, for example, aswitch for selecting one from a plurality of stages of settings such asshort distance/medium distance/long distance. The lane change assistswitch 176 is a switch for instructing (accepting) the start of a lanechange when the control device 19 confirms the start of the lane changewith the driver. By operating the lane change assist switch 176 for alonger time than a predetermined time after accepting the start of thelane change, the acceptance of the lane change proposed by the controldevice 19 can be revoked.

Additionally or alternatively to the set of button switches illustratedin FIG. 2, a direction indicator lever for the direction indicators or aswitch of other onboard equipment 14 can be used as the input device 17.For example, in a case in which the control device 19 proposes whetheror not to automatically change lanes, when the driver operates thedirection indicator lever, the lane change is performed toward thedirection in which the direction indicator lever is operated, ratherthan the proposed lane change. The input device 17 outputs the inputsetting information to the control device 19.

The drive control device 18 controls travel of the subject vehicle. Forexample, when the subject vehicle travels at a constant set speed usingthe autonomous speed control function, the drive control device 18controls the operation of the drive mechanism and the brake operationfor achieving the acceleration/deceleration and the traveling speed sothat the speed of the subject vehicle becomes the set speed.Additionally or alternatively, also when the subject vehicle travels tofollow a preceding vehicle using the autonomous speed control function,the drive control device 18 controls the operations of the drivemechanism and brake in a similar manner to the above. The control of theoperation of the drive mechanism includes controlling the operation ofan internal-combustion engine in the case of an engine car andcontrolling the operation of an electric motor for travel in the case ofan electric car. In the case of a hybrid car, the control of theoperation of the drive mechanism includes controlling the torquedistribution for an internal-combustion engine and an electric motor fortravel.

The drive control device 18 controls the operation of the steeringactuator using the autonomous steering control function in addition tothe above-described control of the operations of the drive mechanism andbrake and thereby executes the steering control of the subject vehicle.For example, when executing the lane keeping control using theautonomous steering control function, the drive control device 18detects lane marks of a subject vehicle lane for the subject vehicle totravel and controls the traveling position of the subject vehicle in theroad width direction so that the subject vehicle travels at a certainposition in the subject vehicle lane. Additionally or alternatively,when executing a lane change assist function, overtaking assistfunction, or route traveling assist function, which will be describedlater, using the autonomous steering control function, the drive controldevice 18 controls the traveling position of the subject vehicle in theroad width direction so that the subject vehicle changes lanes.Additionally or alternatively, when executing a right or left turnassist function using the autonomous steering control function, thedrive control device 18 performs the travel control of turning right orleft at an intersection or the like. The drive control device 18controls the travel of the subject vehicle in accordance with commandsfrom the control device 19, which will be described below. Any of otherknown methods can also be used as the travel control method executed bythe drive control device 18.

The control device 19 includes a read only memory (ROM) that storesprograms for controlling the travel of the subject vehicle, a centralprocessing unit (CPU) that executes the programs stored in the ROM, arandom access memory (RAM) that serves as an accessible storage device,etc. As substitute for or in addition to the CPU, a micro processingunit (MPU), a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), orthe like can be used as the operation circuit.

The control device 19 executes the programs stored in the ROM using theCPU thereby to achieve a travel information acquisition function ofacquiring information regarding a traveling state of the subject vehicleand an autonomous travel control function of autonomously controllingthe traveling speed and/or steering of the subject vehicle. The travelinformation acquisition function of the control device 19 is a functionused for acquiring the travel information regarding the traveling stateof the subject vehicle. For example, the control device 19 uses thetravel information acquisition function to acquire as the travelinformation the external image information around the vehicle capturedby the front camera, rear camera, and side cameras included in thesensors 11. Additionally or alternatively, the control device 19 usesthe travel information acquisition function to acquire as the travelinformation the detection results by the front radar, rear radar, andside radars included in the sensors 11. Additionally or alternatively,the control device 19 uses the travel information acquisition functionto acquire as the travel information the vehicle speed information ofthe subject vehicle detected by the vehicle speed sensor included in thesensors 11 and/or the image information of the driver's face captured bythe onboard camera included in the sensors 11.

Additionally or alternatively, the control device 19 uses the travelinformation acquisition function to acquire as the travel informationthe current positional information of the subject vehicle from thesubject vehicle position detection device 12. Additionally oralternatively, the control device 19 uses the travel informationacquisition function to acquire as the travel information the setdestination and the route to the destination from the navigation device15. Additionally or alternatively, the control device 19 uses the travelinformation acquisition function to acquire as the travel informationthe positional information of curved roads and the size of the curve(e.g., curvature or radius of curvature), merging points, branchingpoints, tollgates, positions at which the number of lanes decreases,etc. from the map database 13. In addition, the control device 19 usesthe travel information acquisition function to acquire as the travelinformation the information on an operation of the onboard equipment 14performed by the driver from the onboard equipment 14.

The autonomous travel control function of the control device 19 is afunction used for autonomously controlling the travel of the subjectvehicle without depending on the driver's operation. The autonomoustravel control function of the control device 19 includes an autonomousspeed control function used for autonomously controlling the travelingspeed of the subject vehicle and an autonomous steering control functionused for autonomously controlling the steering of the subject vehicle.The autonomous speed control function and autonomous steering controlfunction of the present embodiment will be described below.

«Autonomous Speed Control Function»

The autonomous speed control function is a function used, when detectinga preceding vehicle, for traveling to follow the preceding vehicle whileperforming the inter-vehicle distance control so as to maintain theinter-vehicle distance in accordance with the vehicle speed with anupper limit of the vehicle speed that is set by the driver. On the otherhand, when no preceding vehicle is detected, the autonomous speedcontrol function is used for performing constant speed traveling at avehicle speed that is set by the driver. The former is also referred toas inter-vehicle distance control while the latter is also referred toas constant speed control. The autonomous speed control function mayinclude a function of detecting the speed limit of a traveling road froma road sign using the sensors 11, or acquiring the speed limit from themap information of the map database 13, to automatically set the speedlimit to a set vehicle speed.

To activate the autonomous speed control function, the driver firstoperates the resume/acceleration switch 172 or set/coast switch 173 ofthe input device 17 illustrated in FIG. 2 to input a desired travelingspeed. For example, when the set/coast switch 173 is pressed while thesubject vehicle is traveling at 70 km/h, the current traveling speed isset without any modification, but if the speed desired by the driver is80 km/h, the resume/acceleration switch 172 may be pressed a pluralityof times to increase the set speed. On the contrary, if the speeddesired by the driver is 60 km/h, the set/coast switch 173 may bepressed a plurality of times to decrease the set speed. Theinter-vehicle distance desired by the driver may be selected, forexample, from a plurality of stages of settings such as shortdistance/medium distance/long distance by operating the inter-vehicledistance adjustment switch 175 of the input device 17 illustrated inFIG. 2.

The constant speed control is executed when the front radar or the likeof the sensors 11 detects no preceding vehicle ahead of the subjectvehicle in its lane. In the constant speed control, the drive controldevice 18 controls the operation of the drive mechanism such as theengine and the brake while feeding back the vehicle speed data obtainedby the vehicle speed sensor so as to maintain the set traveling speed.

The inter-vehicle distance control is executed when the front radar orthe like of the sensors 11 detects a preceding vehicle ahead of thesubject vehicle in its lane. In the inter-vehicle distance control, thedrive control device 18 controls the operation of the drive mechanismsuch as the engine and the brake while feeding back the inter-vehicledistance data detected by the front radar so as to maintain the setinter-vehicle distance with an upper limit of the vehicle speed that isset by the driver. If the preceding vehicle stops while the subjectvehicle is traveling under the inter-vehicle distance control, thesubject vehicle also stops following the preceding vehicle. Additionallyor alternatively, if the preceding vehicle starts within 30 secondsafter the subject vehicle stops, the subject vehicle also startstraveling to follow the preceding vehicle again by the inter-vehicledistance control. If the subject vehicle stops for more than 30 seconds,the subject vehicle does not start in an automated or autonomous mannereven when the preceding vehicle starts, and after the preceding vehiclestarts, the subject vehicle starts traveling to follow the precedingvehicle again by the inter-vehicle distance control when theresume/acceleration switch 172 is pressed or the accelerator pedal isdepressed.

«Autonomous Steering Control Function»

The autonomous steering control function is a function used, when apredetermined condition is satisfied during the execution of theabove-described autonomous speed control function, for controlling theoperation of the steering actuator thereby to execute the steeringcontrol of the subject vehicle. This autonomous steering controlfunction includes, for example, a lane keeping function, a lane changeassist function, an overtaking assist function, a route traveling assistfunction, and other functions. The lane keeping function is a functionused for controlling the steering actuator so as to travel near thecenter of the lane, for example, to assist the driver's steeringoperation. The lane keeping function is also referred to as a lane widthdirection maintaining function or the like.

«Lane Change Assist Function»

The lane change assist function serves to turn on the directionindicators when the driver operates the direction indicator lever, asillustrated in FIG. 3, and also serves to start a lane changeperformance (abbreviated as LCP, hereinafter) that is a series ofprocesses for the automated or autonomous lane change when apreliminarily set lane change start condition is satisfied. The lanechange assist function is used for determining whether or not the lanechange start condition is satisfied, based on various travel informationitems acquired using the travel information acquisition function.Examples of the lane change start condition include, but are not limitedto, a condition in which all of the following conditions are satisfied:

-   -   The lane keeping mode is carried out in a hands-on mode;    -   Hands-on determination is made;    -   The vehicle is traveling at a speed of 60 km/h or more;    -   There is a lane in the lane change direction;    -   The lane as the lane change destination includes a space to        which a lane change is possible;    -   The type of lane markers indicates that a lane change is        permitted;    -   The radius of curvature of the road is 250 m or more; and    -   The elapsed time after the driver operates the direction        indicator lever is within one second.

The lane keeping mode in the hands-on mode, which will be describedlater in detail, refers to a state in which the autonomous speed controlfunction and the lane keeping function of the autonomous steeringcontrol function are being executed and the holding of the steeringwheel by the driver is detected. The hands-on determination being maderefers to a state in which the driver continues to hold the steeringwheel.

The lane change assist function is used for starting the LCP when thelane change start condition is satisfied. The LCP includes lateralmovement of the subject vehicle to an adjacent lane and lane changemaneuver (abbreviated as LCM, hereinafter) for actually moving to theadjacent lane. During the execution of the LCP, the lane change assistfunction serves to control the presentation device 16 to present thedriver with information indicating that the lane change is performed inan automated or autonomous manner and also serves to call attention tothe surroundings. When the LCM is completed, the lane change assistfunction is used for turning off the direction indicators and startingthe execution of the lane keeping function in the adjacent lane.

«Overtaking Assist Function»

The overtaking assist function is used for controlling the presentationdevice 16 to present the driver with overtaking information when apreceding vehicle slower than the subject vehicle is present ahead ofthe subject vehicle in its lane, as illustrated in FIG. 4, and apredetermined overtaking proposal condition that is preliminarily set issatisfied. Here, the overtaking information refers to information forproposing to overtake a preceding vehicle to the driver. The overtakingassist function serves to start the above-described LCP when the driveroperates the lane change assist switch 176 of the input device 17 foracceptance (corresponding to the acceptance input) in response to thepresentation of the overtaking information and an overtaking startcondition that is preliminarily set is satisfied. The overtaking assistfunction serves to determine, based on various travel information itemsacquired using the travel information acquisition function, whether ornot the overtaking proposal condition and the overtaking start conditionare satisfied.

Examples of the overtaking proposal condition include, but are notlimited to, a condition in which all of the following conditions aresatisfied:

-   -   The lane keeping mode is carried out in a hands-off mode;    -   The vehicle is traveling at a speed of 60 km/h or more;    -   There is a lane in the lane change direction;    -   The lane as the lane change destination includes a space to        which a lane change is possible after 5 seconds;    -   The type of lane markers indicates that a lane change is        permitted;    -   The radius of curvature of the road is 250 m or more;    -   The speed of the subject vehicle is slower than the set speed by        5 km/h or more;    -   The speed of the preceding vehicle is slower than the set speed        by 10 km/or more;    -   The distance between the subject vehicle and the preceding        vehicle is less than a threshold that is preliminarily set based        on the speed difference between the subject vehicle and the        preceding vehicle; and    -   The speed of the preceding vehicle present in the lane as the        lane change destination satisfies a predetermined condition.

The lane keeping mode in the hands-off mode, which will be describedlater in detail, refers to a mode in which the autonomous speed controlfunction and the lane keeping function of the autonomous steeringcontrol function are being executed and the holding of the steeringwheel by the driver is not necessary. The condition that the speed ofthe preceding vehicle present in the lane as the lane change destinationsatisfies a predetermined condition is applied differently depending onthe type of the lane as the lane change destination. For example, whenchanging lanes from the left-side lane to the right-side lane on amulti-lane road with left-hand traffic, the condition is that the speedof the subject vehicle present in the left-side lane is higher than thespeed of the preceding vehicle present in the right-side lane by about 5km/h. On the contrary, when changing lanes from the right-side lane tothe left-side lane on a multi-lane road with left-hand traffic, thecondition is that the speed difference between the subject vehicle andthe preceding vehicle in the left-side lane is within about 5 km/h. Theconditions regarding the relative speed difference between the subjectvehicle and the preceding vehicle are reversed on a right-hand trafficroad.

The overtaking assist function serves to turn on the directionindicators to start the LCP when the driver accepts the presentation ofthe overtaking information and a predetermined overtaking startcondition that is preliminarily set is satisfied. Examples of theovertaking start condition include, but are not limited to, a conditionin which all of the following conditions are satisfied:

The lane keeping mode is carried out in the hands-on mode;

-   -   Hands-on determination is made;    -   The vehicle is traveling at a speed of 60 km/h or more;    -   There is a lane in the lane change direction;    -   The lane as the lane change destination includes a space to        which a lane change is possible;    -   The type of lane markers indicates that a lane change is        permitted;    -   The radius of curvature of the road is 250 m or more;    -   The speed of the subject vehicle is slower than the set speed by        5 km/h or more (when changing lanes to the right-side lane in a        left-hand traffic);    -   The speed of the preceding vehicle is slower than the set speed        by 10 km/or more (when changing lanes to the right-side lane in        a left-hand traffic);    -   The speed of the preceding vehicle present in the lane as the        lane change destination satisfies a predetermined condition; and    -   The elapsed time after the operation of the lane change assist        switch 176 is within 10 seconds.

The condition that the speed of the preceding vehicle is slower than theset speed by 10 km/or more can be changed by the driver's setting, andthe set speed after the change represents the overtaking startcondition. As the speed that can be changed, for example, 15 km/h and 20km/h can be selected in addition to 10 km/h. The condition that thespeed of the preceding vehicle present in the lane as the lane changedestination satisfies a predetermined condition is the same as that inthe above-described overtaking proposal condition.

The overtaking assist function serves to start the LCP when theovertaking start condition is satisfied, and also serves to execute thelateral movement to an adjacent lane and the LCM. During the executionof the LCP, the overtaking assist function serves to control thepresentation device 16 to present the driver with information indicatingthat the lane change is performed in an automated or autonomous mannerand also serves to call attention to the surroundings. When the LCM iscompleted, the overtaking assist function is used for turning off thedirection indicators and starting the execution of the lane keepingfunction in the adjacent lane. When the overtaking proposal condition issatisfied again after overtaking the preceding vehicle, the overtakingassist function is used for controlling the presentation device 16 topropose to return to the original lane to the driver. When the driveraccepts this proposal by operating the lane change assist switch 176 ofthe input device 17 and the overtaking start condition is satisfied, theovertaking assist function serves to start the LCP so that the subjectvehicle returns to the original lane.

«Route Traveling Assist Function»

The route traveling assist function serves to control the presentationdevice 16 to present the route traveling information when there is atraveling direction change point such as a branching point, a mergingpoint, an exit, or a toll gate on the set route, the distance to thetraveling direction change point is within a predetermined distance, anda predetermined route traveling proposal condition is satisfied and alsoserves to propose a lane change to the traveling direction change point.In addition, the route traveling assist function serves to start the LCPwhen the proposal of the lane change is accepted through the operationof the lane change assist switch 176 and a predetermined route travelingstart condition is satisfied. The route traveling assist function isused for determining, based on various travel information items acquiredusing the travel information acquisition function, whether or not theroute traveling proposal condition and the route traveling startcondition are satisfied.

When the route is set by the navigation device 15, but the routetraveling assist function is not executed or is disabled in the setting,the navigation device 15 executes a normal navigation function thatserves to guide the route.

FIG. 6 illustrates an example in which when traveling in the right-sidelane on a left-hand traffic road with three lanes on each side, thesubject vehicle sequentially changes lanes twice toward a branchingpoint existing in the left-side lane and moves from the branching pointto a branching road extending on the left side of the left-side lane.When the location is within a first predetermined distance to thebranching point (e.g., about 2.5 km to 1.0 km before the branchingpoint) and the route traveling proposal condition is satisfied, theroute traveling assist function serves to propose a lane change from theright-side lane to the central lane based on the route travelinginformation. The first predetermined distance (also referred to as alane change proposal section) is preliminarily set in accordance withthe number of lane changes required to move to the lane in which thetraveling direction change point is present. For example, as illustratedin FIG. 6, when it is necessary to change lanes twice from theright-side lane to the left-side lane via the central lane, the sectionof 2.5 km to 1.0 km before the branching point represents the firstpredetermined distance (lane change proposal section).

Examples of the route traveling proposal condition include, but are notlimited to, a condition in which all of the following conditions aresatisfied:

-   -   A destination is set by the navigation device 15;    -   The lane keeping mode is carried out in the hands-off mode;    -   The vehicle is traveling at a speed of 60 km/h or more;    -   There is a lane in the lane change direction;    -   The type of lane markers indicates that a lane change is        permitted; and    -   The radius of curvature of the road is 250 m or more.

In the route traveling proposal condition, even when the lane as thelane change destination does not include a space to which a lane changeis possible, the route traveling information is presented in order tonotify the driver that a lane change along the route is necessary.

The route traveling assist function serves to turn on the directionindicators to start the LCP when the driver accepts the lane change forheading to the branching point and the route traveling start conditionis satisfied. Examples of the route traveling start condition include,but are not limited to, a condition in which all of the followingconditions are satisfied:

-   -   The lane keeping mode is carried out in the hands-on mode;    -   Hands-on determination is made;    -   The vehicle is traveling at a speed of 60 km/h or more;    -   There is a lane in the lane change direction;    -   The lane as the lane change destination includes a space to        which a lane change is possible;    -   The type of lane markers indicates that a lane change is        permitted;    -   The vehicle is traveling in the lane change proposal section;        and    -   The radius of curvature of the road is 250 m or more.

The route traveling assist function serves to start the LCP when theroute traveling start condition is satisfied, and also serves to executethe lateral movement to the central lane and the LCM. When the LCM iscompleted, the route traveling assist function is used for turning offthe direction indicators and starting the execution of the lane keepingfunction in the central lane. During the execution of the LCP, the routetraveling assist function serves to control the presentation device 16to present the driver with information indicating that the lane changeis performed in an automated or autonomous manner and also serves tocall attention to the surroundings.

As illustrated in FIG. 6, during the execution of the lane keepingfunction in the central lane, when the location is within a secondpredetermined distance to the branching point (e.g., about 2.3 km to 700m before the branching point) and the route traveling start condition issatisfied, the route traveling assist function is used for turning onthe direction indicators to start the second LCP and performing the lanechange from the central lane to the left-side lane. When the second LCMis completed, the route traveling assist function is used for turningoff the direction indicators and starting the execution of the lanekeeping function in the left-side lane.

During the execution of the lane keeping function in the left-side lane,when the location is within a third predetermined distance to thebranching point (e.g., about 800 m to 150 m before the branching point)and the route traveling start condition is satisfied, the routetraveling assist function serves to turn on the direction indicators. Inaddition, the route traveling assist function serves to start theautonomous steering control from a point beyond the branching point tothe branching road and perform a lane change from the left-side lane tothe branching road. When the lane change to the branching road iscompleted, the route traveling assist function is used for turning offthe direction indicators and starting the execution of the lane keepingfunction in the branching road.

FIG. 7 is a block diagram illustrating a state transition of eachfunction established in the control device 19. The system illustrated inthe figure means an autonomous travel control system realized by thecontrol device 19. When the main switch 171 of FIG. 2 is turned ON fromthe system OFF state illustrated in the figure, the system comes to astandby state. From this standby state, the autonomous speed control isactivated by turning ON the set/coast switch 173 or resume/accelerationswitch 172 of FIG. 2. This allows the above-described constant speedcontrol or inter-vehicle distance control to be started, and the drivercan drive the subject vehicle simply by operating the steering wheelwithout stepping on the accelerator or the brake.

During the execution of the autonomous speed control, when the condition(1) of FIG. 7 is satisfied, the mode transitions to the lane keepingmode of the autonomous steering control/hands-on mode. Examples of thecondition (1) include, but are not limited to, a condition in which allof the following conditions are satisfied:

-   -   Lane markers on both sides of the subject vehicle are being        detected;    -   The driver is holding the steering wheel;    -   The vehicle is traveling near the center of the lane;    -   The direction indicators are not operating;    -   The windshield wiper is not operating at a high speed (HI); and    -   When a high-precision map is provided, there is not a tollgate,        an exit, a merging point, an intersection, or a point at which        the number of lanes decreases, within about 200 m ahead.

The hands-on mode refers to a mode in which the autonomous steeringcontrol does not operate unless the driver holds the steering wheel,while the hands-off mode refers to a mode in which the autonomoussteering control operates even when the driver releases the steeringwheel. The holding of the steering wheel by the driver is detected usinga touch sensor of the sensors 11.

During the execution of the lane keeping mode of the autonomous steeringcontrol/hands-on mode, when the condition (2) of FIG. 7 is satisfied,the mode transitions to the lane keeping mode of the autonomous steeringcontrol/hands-off mode. Examples of the condition (2) include acondition in which all of the following conditions are satisfied:

-   -   The subject vehicle is traveling on an automobile road;    -   The vehicle is traveling on a road that is structurally        separated from the oncoming lane;    -   The vehicle is traveling on a road for which a high-precision        map is prepared;    -   The vehicle is traveling at a speed not higher than the speed        limit;    -   GPS signals are effective;    -   The driver is holding the steering wheel;    -   The driver is facing forward;    -   There is not a tollgate, an exit, a merging point, an        intersection, or a point at which the number of lanes decreases,        within about 800 m ahead;    -   There is not a sharp curve of 100 R or less within about 500 m        ahead;    -   The vehicle is not traveling in a tunnel that exceeds 500 m from        the tunnel entrance; and    -   The accelerator pedal is not depressed.

Whether or not the driver is facing forward is determined, for example,based on an image captured by a driver monitor camera of the sensors 11.

On the contrary, during the execution of the lane keeping mode of theautonomous steering control/hands-off mode, when the condition (3) ofFIG. 7 is satisfied, the mode transitions to the lane keeping mode ofthe autonomous steering control/hands-on mode. Examples of the condition(3) include, but are not limited to, a condition in which any of thefollowing conditions is satisfied:

-   -   The subject vehicle is traveling on a road other than an        automobile road;    -   The vehicle is traveling in a two-way traffic section;    -   The vehicle is traveling on a road for which no high-precision        map is prepared;    -   The vehicle is traveling at a speed higher than the speed limit;    -   GPS signals can no longer be received;    -   The driver does not face forward within 5 seconds after a        forward gaze alarm is activated;    -   The driver monitor camera can no longer detect the driver;    -   There is any of a tollgate, an exit, a merging point, an        intersection, or a point at which the number of lanes decreases,        within about 800 m ahead;    -   When traveling at a vehicle speed of less than about 40 km/h,        there is a sharp curve of 100 R or less within about 200 m        ahead;    -   When traveling at a vehicle speed of about 40 km/h or more,        there is a sharp curve of 170 R or less within about 200 m        ahead;    -   The vehicle is traveling in a tunnel that exceeds 500 m from the        tunnel entrance;    -   The driver is stepping on the accelerator pedal while holding        the steering wheel; and    -   An approaching alarm is operating.

During the execution of the lane keeping mode of the autonomous steeringcontrol/hands-off mode, when the condition (4) of FIG. 7 is satisfied,the autonomous steering control is stopped and transitions to theautonomous speed control. Examples of the condition (4) include, but arenot limited to, a condition in which any of the following conditions issatisfied:

-   -   Lane markers on both sides of the subject vehicle are no longer        detected for a certain period of time;    -   The driver is operating the steering wheel; and    -   The windshield wiper is operating at a high speed (HI).

The driver's steering wheel operation is determined by detecting thetorque applied to the steering wheel.

During the execution of the lane keeping mode of the autonomous steeringcontrol/hands-off mode, when the condition (5) of FIG. 7 is satisfied,the autonomous steering control and the autonomous speed control arestopped and transition to the standby state. Examples of the condition(5) include, but are not limited to, a condition in which any of thefollowing conditions is satisfied:

-   -   The driver has operated the brake;    -   The driver has operated the cancel switch 174 of FIG. 2;    -   One or more doors of the subject vehicle have opened;    -   The driver's seat belt has been released;    -   The seating sensor has detected that the driver is no longer on        the driver's seat;    -   The select lever has come to other than “D” or ““M”;    -   The parking brake has been operated;    -   The antiskid brake system of the vehicle has been turned OFF;    -   The antiskid brake system has operated;    -   The snow mode has been turned ON;    -   The emergency brake has operated;    -   The stop state continues for about 3 minutes after the vehicle        has stopped due to the vehicle speed control;    -   The front camera has detected poor visibility such as being        unable to correctly recognize an object due to dirt, backlight,        rain/fog, or the like;    -   The front radar has detected shielding or radio disturbance;    -   The front radar has detected an axis deviation;    -   The side radar has detected shielding or radio disturbance; and    -   The side radar has detected an axis deviation.

During the execution of the autonomous steering control/hands-on mode,when the condition (6) of FIG. 7 is satisfied, the autonomous steeringcontrol is stopped and transitions to the autonomous speed control.Examples of the condition (6) include, but are not limited to, acondition in which any of the following conditions is satisfied:

-   -   Lane markers on both sides of the subject vehicle are no longer        detected;    -   The driver has operated the steering wheel;    -   The driver has operated the direction indicator lever;    -   The windshield wiper has operated at a high speed (HI)    -   The vehicle has come to a tollgate section when a high-precision        map is prepared; and    -   The front camera has detected poor visibility such as being        unable to correctly recognize an object due to dirt, backlight,        rain/fog, or the like.

During the execution of the autonomous steering control/hands-on mode,when the condition (7) of FIG. 7 is satisfied, the autonomous steeringcontrol and the autonomous speed control are stopped and transition tothe standby state. Examples of the condition (7) include, but are notlimited to, a condition in which any of the following conditions issatisfied:

-   -   The driver has operated the brake;    -   The driver has operated the cancel switch 174 of FIG. 2;    -   One or more doors of the subject vehicle have opened;    -   The driver's seat belt has been released;    -   The seating sensor has detected that the driver is no longer on        the driver's seat;    -   The select lever has come to other than “D” or ““M”;    -   The parking brake has been operated;    -   The antiskid brake system of the vehicle has been turned OFF;    -   The antiskid brake system has operated;    -   The snow mode has been turned ON;    -   The emergency brake has operated;    -   The stop state continues for about 3 minutes after the vehicle        has stopped due to the vehicle speed control;    -   The front radar has detected shielding or radio disturbance; and    -   The front radar has detected an axis deviation.

During the execution of the autonomous speed control, when the condition(8) of FIG. 7 is satisfied, the control transitions to the standbystate. Examples of the condition (8) include, but are not limited to, acondition in which any of the following conditions is satisfied:

-   -   The driver has operated the brake;    -   The driver has operated the cancel switch 174 of FIG. 2;    -   One or more doors of the subject vehicle have opened;    -   The driver's seat belt has been released;    -   The seating sensor has detected that the driver is no longer on        the driver's seat;    -   The select lever has come to other than “D” or ““M”;    -   The parking brake has been operated;    -   The antiskid brake system of the vehicle has been turned OFF;    -   The antiskid brake system has operated;    -   The snow mode has been turned ON;    -   The emergency brake has operated;    -   The stop state continues for about 3 minutes after the vehicle        has stopped due to the vehicle speed control;    -   The front radar has detected shielding or radio disturbance; and    -   The front radar has detected an axis deviation.

During the execution of the lane keeping mode of the autonomous steeringcontrol/hands-off mode, when the condition (9) of FIG. 7 is satisfied,the mode transitions to a lane change mode of the autonomous steeringcontrol/hands-on mode. Examples of the condition (8) include, but arenot limited to, a condition in which any of the following conditions issatisfied:

-   -   The system has proposed a lane change based on the overtaking        assist function or the route traveling assist function and the        driver has operated the lane change assist switch 176; and    -   The driver has operated the direction indicator lever to execute        the lane change assist function.

During the execution of the lane change mode of the autonomous steeringcontrol/hands-on mode, when the condition (10) of FIG. 7 is satisfied,the mode transitions to the lane keeping mode of the autonomous steeringcontrol/hands-on mode. Examples of the condition (10) include, but arenot limited to, a condition in which any of the following conditions issatisfied:

-   -   The speed limit has been exceeded before the start of the LCP;    -   The driver has stepped on the accelerator pedal while holding        the steering wheel before the start of the LCP;    -   The LCP can no longer be started within 10 seconds after        pressing the lane change assist switch 176 during the proposal        of a lane change when there is a slow car ahead;    -   The LCP can no longer be started and the vehicle has come too        close to the branching point after pressing the lane change        assist switch 176 during the proposal of a lane change to travel        along the route;    -   The LCM can no longer be started within 5 seconds after the LCP        has operated;    -   The vehicle speed has fallen below about 50 km/h after starting        the LCP and before starting the LCM;    -   There is no longer a space in the adjacent lane required to        change lanes after operating the LCP and before starting the        LCM;    -   The driver has performed a cancel operation before starting the        LCM;    -   Lane markers can no longer be detected before starting the LCM;    -   A determination has been made before starting the LCM that there        is no adjacent lane in the direction of changing lanes or there        will be no adjacent lane within a certain distance ahead;    -   A determination has been made before starting the LCM that there        is a curve with a radius of curvature of 250 m or more within a        certain distance ahead;    -   A determination has been made before starting the LCM that there        is a section within a certain distance ahead in which the type        of lane marking prohibits a lane change to the adjacent lane;    -   The side radar has detected shielding or radio disturbance        before starting the LCM;    -   The side radar has detected an axis deviation before starting        the LCM;    -   The hands-on alarm has operated;    -   The driver has stopped the direction indicators; and    -   The LCP has been completed.

The hands-on alarm operates when any of the following conditions issatisfied:

-   -   The driver does not hold the steering wheel within about 2        seconds after the LCP has operated;    -   The driver does not hold the steering wheel within about 2        seconds after pressing the lane change assist switch 176 during        the proposal of a lane change when there is a slow car ahead;        and    -   The driver does not hold the steering wheel within about 2        seconds after pressing the lane change assist switch 176 during        the proposal of a lane change to travel along the route.

The system is turned OFF when the main switch 171 is turned OFF in anyof the autonomous steering control/hands-off mode, the autonomoussteering control/hands-on mode, the autonomous speed control, and thestandby state.

The travel control process according to the present embodiment will thenbe described with reference to FIG. 8. FIG. 8 is a flowchartillustrating the travel control process according to the presentembodiment. The control device 19 executes the travel control process,which will be described below, at predetermined time intervals. Thefollowing description will be made on the assumption that the controldevice 19 uses the autonomous travel control function to execute theautonomous speed control and the autonomous steering control and alsouses the lane change assist function, the overtaking assist function,and the route traveling assist function to execute the lane changeassist control, the overtaking assist control, and the route travelingassist control, respectively.

First, in step S1 of FIG. 8, a determination is made as to whether ornot the main switch 171 of the control device 19 is ON, and when themain switch 171 is OFF, step S1 is repeated until the main switch 171 isturned ON. When the main switch 171 is ON, the process proceeds to stepS2, in which a determination is made as to whether or not the travelingspeed is set by the driver. When the traveling speed is not set, theprocess returns to step S1, from which steps S1 and S2 are repeateduntil the traveling speed is set. The setting of the traveling speed isperformed by the driver operating the resume/acceleration switch 172 orset/coast switch 173 of the input device 17 illustrated in FIG. 2 toinput a desired traveling speed.

When the traveling speed is set, the autonomous speed control isstarted. In step S3, the front radar (of the sensors 11) which detectsan obstacle ahead of the subject vehicle is used to detect whether ornot there is a preceding vehicle ahead of the subject vehicle in itstraveling lane, and when there is a preceding vehicle, the processproceeds to step S4, in which the inter-vehicle distance control isexecuted. When there is no preceding vehicle, the process proceeds tostep S5, in which the constant speed control is executed. This allowsthe driver to drive the subject vehicle at a desired speed simply byoperating the steering wheel without stepping on the accelerator or thebrake.

During the execution of the inter-vehicle distance control in step S4 orthe constant speed control in step S5, a determination is made in stepS6 as to whether or not the above-described condition (1) fortransitioning to the lane keeping mode of the autonomous steeringcontrol/hands-on mode is satisfied. When the condition (1) is satisfied,the process proceeds to step S7, while when the condition (1) is notsatisfied, the process returns to step S3.

In step S7, the front radar (of the sensors 11) which detects anobstacle ahead of the subject vehicle is used to detect whether or notthere is a preceding vehicle ahead of the subject vehicle in itstraveling lane. When there is a preceding vehicle, the process proceedsto step S8, in which the inter-vehicle distance control/lane keepingmode is executed. When there is no preceding vehicle, the processproceeds to step S9, in which the constant speed control/lane keepingmode is executed.

During the execution of the inter-vehicle distance control/lane keepingmode in step S8 or the constant speed control/lane keeping mode in stepS9, a determination is made in the subsequent step S10 as to whether ornot the above-described condition (2) for transitioning to theautonomous steering control/hands-off mode is satisfied. When thecondition (2) is satisfied, the process proceeds to step S11, while whenthe condition (2) is not satisfied, the process returns to step S3. Instep S11 in which the condition (2) for transitioning to the autonomoussteering control/hands-off mode is satisfied, the front radar (of thesensors 11) which detects an obstacle ahead of the subject vehicle isused to detect whether or not there is a preceding vehicle ahead of thesubject vehicle in its traveling lane. When there is a precedingvehicle, the process proceeds to step S12, in which the inter-vehicledistance control/lane keeping mode/hands-off is executed. When there isno preceding vehicle, the process proceeds to step S13, in which theconstant speed control/lane keeping mode/hands-off is executed.

In step S14, a determination is made as to whether or not the directionindicator lever has been operated by the driver. When the directionindicator lever has been operated, the condition (9) for transitioningto the lane changing mode of the autonomous steering control/hands-onmode is satisfied, and the process proceeds to step S15. In step S15,the lane change assist control is executed. When the lane change assistcontrol in step S15 is completed, the process returns to step S3. Whenthe direction indicator lever has not been operated by the driver instep S14, the process proceeds to step S16.

In step S16, a determination is made as to whether or not there is apreceding vehicle slower than the set speed. When there is a precedingvehicle slower than the set speed, a determination is made as to whetheror not the condition (9) is satisfied, and when the condition (9) issatisfied, the mode transitions to the lane change mode of theautonomous steering control/hands-on mode, and the process proceeds tostep S17. In step S17, the overtaking assist control is executed. Whenthe overtaking assist control in step S17 is completed, the processreturns to step S3. When there is no preceding vehicle slower than theset speed in step S16, the process proceeds to step S18.

In step S18, a determination is made as to whether a route to thedestination is set in the navigation device 15. When no route is set,the process returns to step S1. When a route to the destination is setin the navigation device 15 in step S18, the process proceeds to stepS19. In step S19, a determination is made as to whether or not apredetermined distance to the traveling direction change point such as abranching point existing on the route is reached. When the predetermineddistance to the traveling direction change point is reached in step S19,a determination is made as to whether or not the condition (9) issatisfied, and when the condition (9) is satisfied, the mode transitionsto the lane change mode of the autonomous steering control/hands-onmode, and the process proceeds to step S20. In step S20, the routetraveling assist control is executed. When the route traveling assistcontrol in step S20 is completed, the process returns to step S3. Whenthe predetermined distance to the traveling direction change point isnot reached in step S19, the process returns to step S1.

In the flowchart of FIG. 8, the necessities of the lane change assistcontrol, the overtaking assist control, and the route traveling assistcontrol are determined in this order, but in practice, the necessitiesof these control procedures are determined in parallel, and when, duringany of the assist control procedures is being executed, it becomesnecessary to execute another assist control procedure, the necessity ofexecution is arbitrated between the assist control procedures, and theassist control to be executed preferentially is determined.

First Embodiment

The description will then be directed to a first embodiment for solvinga problem that may occur in the basic processing of the travel controldescribed in the flowchart of FIG. 8. In the route traveling assistcontrol of the travel control process described in the flowchart of FIG.8, as illustrated in FIG. 9, for example, when the subject vehicle istraveling in the left-side lane including a lane change point in orderto perform a lane change from the branching point to the branching roadusing the route traveling assist function, if a preceding vehicle thatis slower than the set speed of the autonomous speed control appearsahead of the subject vehicle, the overtaking assist function may beexecuted. When the proposal of overtaking using the overtaking assistfunction is made near the branching point and the driver accepts theproposal of overtaking, the subject vehicle may perform a lane changefrom the left-side lane to the central lane or the right-side lane inorder to overtake the preceding vehicle. Thus, when the lane change isperformed using the overtaking assist function near the branching point,it may not be possible to return to the left-side lane and head to thebranching point depending on the road congestion or the like.

In the present embodiment, to prevent the occurrence of theabove-described problem, as illustrated in FIG. 10, a presentationprohibition point for the overtaking information is set at a positionbefore the branching point by a presentation prohibition distance Dv. Inaddition, when the distance from the subject vehicle to the travelingdirection change point such as the branching point is shorter than thepredetermined presentation prohibition distance Dv, control is performedso as not to perform the presentation of the overtaking informationusing the overtaking assist function. In the embodiment illustrated inFIG. 6, for example, the presentation prohibition distance Dv may be setto the first predetermined distance (e.g., about 2.5 km before thetraveling direction change point) in which the route travelinginformation is presented when moving from the right-side lane to theleft-side lane of a three-lane road.

The travel control process according to the present embodiment will thenbe described with reference to FIG. 11. FIG. 11 is a flowchartillustrating the travel control process according to the presentembodiment. When the overtaking assist function of the control device 19serves to determine in step S30 that a preceding vehicle that is slowerthan the set speed of the autonomous speed control is present ahead ofthe subject vehicle, the process proceeds to step S31. In step S31, thepositional information of the subject vehicle is acquired from thesensors 11, the map information is acquired from the map database 13,and the set route information is acquired from the navigation device 15.The overtaking assist function of the control device 19 is used forcalculating the distance from the subject vehicle to the nearesttraveling direction change point based on the acquired informationitems. The overtaking assist function of the control device 19 serves tocompare the calculated distance to the traveling direction change pointwith the presentation prohibition distance Dv. When the distance to thetraveling direction change point is shorter than the presentationprohibition distance Dv, the process proceeds to step S32, in which thepresentation of the overtaking information is prohibited. On thecontrary, when the distance to the traveling direction change point islonger than the presentation prohibition distance Dv in step S31, theprocess proceeds to step S33, in which the control device 19 executesthe overtaking assist control.

Second Embodiment

In the first embodiment, the predetermined distance is used as thepresentation prohibition distance Dv, but the presentation prohibitiondistance Dv may be changed in accordance with whether or not the routeis set and/or whether the route traveling assist function isenabled/disabled. The travel control process according to the presentembodiment will be described below with reference to FIG. 12. FIG. 12 isa flowchart illustrating a procedure of setting the presentationprohibition distance Dv in the present embodiment.

In step S40, the overtaking assist function of the control device 19 isused for confirming whether or not the route to the destination is setin the navigation device 15. When the route to the destination is set inthe navigation device 15, the process proceeds to step S41, in which theovertaking assist function of the control device 19 serves to confirmwhether or not the setting of the route traveling assist function isenabled. When the setting of the route traveling assist function isenabled, the process proceeds to step S42, in which the overtakingassist function of the control device 19 serves to set the presentationprohibition distance Dv to a first presentation prohibition distance da.

When the setting of the route traveling assist function is disabled instep S41, the process proceeds to step S43, in which the overtakingassist function of the control device 19 serves to set the presentationprohibition distance Dv to a second presentation prohibition distancedb. When the route to the destination is not set in the navigationdevice 15 in step S40, the process proceeds to step S44, in which theovertaking assist function of the control device 19 serves to set thepresentation prohibition distance Dv to a third presentation prohibitiondistance dc.

The relationships between the first presentation prohibition distanceda, the second presentation prohibition distance db, and the thirdpresentation prohibition distance dc are da>db>dc, for example, da=2500m, db=300 m, and dc=0 m. The lane change of the subject vehicle isperformed using the route traveling assist function, and therefore thefirst presentation prohibition distance da is set to be the same as thepresentation prohibition distance of the first embodiment thereby toallow the subject vehicle to reliably head to the traveling directionchange point. The second presentation prohibition distance db is set tobe significantly shorter than the first presentation prohibitiondistance da because the driver performs the steering in accordance withthe route guidance provided using the navigation function of thenavigation device 15 and therefore even when the overtaking informationis presented at a position close to the traveling direction changepoint, the lane change can be performed with a short distance. The thirdpresentation prohibition distance dc is set such that the presentationof the overtaking information is possible even at the travelingdirection change point because the route is not set and the routetraveling assist function is disabled; therefore, the driver performsthe steering of the subject vehicle with his/her own intention and maynot necessarily perform the lane change at the traveling directionchange point.

In the second embodiment, the presentation prohibition distance Dv isset in accordance with whether or not the route is set and/or whetherthe route traveling assist function is enabled/disabled, but thepresentation prohibition distance Dv may be set in accordance with thenumber of lane changes required to move from the traveling lane of thesubject vehicle to the lane including the traveling direction changepoint. Also in this case, the presentation prohibition distance Dv ispreferably set to the above-described second presentation prohibitiondistance db or more so that the lane change can be safely performedtoward the traveling direction change point.

As described above, according to the travel control apparatus 1 andtravel control method for a vehicle of the present embodiments, in thecase in which the driver is presented with overtaking information as towhether or not to accept execution of an overtaking assist function forthe vehicle, which is traveling on a route to a preliminarily setdestination, to overtake a preceding vehicle by changing lanes throughautonomous travel control, when the distance from the vehicle to atraveling direction change point is shorter than a preliminarily setpresentation prohibition distance, the presentation of the overtakinginformation is not performed; therefore, the presentation prohibitiondistance is appropriately set and the overtaking information can therebybe prohibited from being presented at the timing when the travelingalong the route is hindered. This can prevent the occurrence of asituation in which the driver inadvertently accepts the presentation ofthe overtaking information for the execution of a lane change and cannothead to the traveling direction change point due to road congestion orthe like.

Moreover, in the case in which a navigation function of presenting theroute and guiding to the destination and a route traveling assistfunction of controlling the vehicle to travel along the route byautonomous travel control are provided, when the route traveling assistfunction is executed, a first presentation prohibition distance is setas the presentation prohibition distance, and when the navigationfunction is executed, a second presentation prohibition distance shorterthan the first presentation prohibition distance is set as thepresentation prohibition distance; therefore, in the case in which thedriver performs the steering of the vehicle based on the route guidanceprovided using the navigation function, even when the overtakinginformation is presented at a position close to the traveling directionchange point, the driver's intention can be reflected as much aspossible to execute the overtaking assist function.

Furthermore, when neither the navigation function nor the routetraveling assist function is executed, a third presentation prohibitiondistance shorter than the second presentation prohibition distance isset as the presentation prohibition distance; therefore, even when theovertaking information is presented at a position close to the travelingdirection change point, the driver's intention can be reflected as muchas possible to execute the overtaking assist function. In addition, thetraveling direction change point includes at least one of a branchingpoint, a merging point, an exit from a road, or a tollgate; therefore,even when it is necessary to change lanes at various traveling directionchange points in order to travel along the route, it is possible toprevent the occurrence of a situation in which the driver inadvertentlyaccepts the presentation of the overtaking information and cannot headto the traveling direction change points.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Travel control apparatus-   11 Sensors-   12 Subject vehicle position detection device-   13 Map database-   14 Onboard equipment-   15 Navigation device-   16 Presentation device-   17 Input device-   171 Main switch-   172 Resume/acceleration switch-   173 Set/coast switch-   174 Cancel switch-   175 Inter-vehicle distance adjustment switch-   176 Lane change assist switch-   18 Drive control device-   19 Control device.

The invention claimed is:
 1. A travel control method for a vehicle,comprising: presenting overtaking information as to whether or not toaccept execution of an overtaking assist function for overtaking apreceding vehicle by changing lanes through autonomous travel control ofthe vehicle traveling on a route to a preliminarily set destination;when a route traveling assist function of controlling the vehicle toautonomously travel along the route is executed, setting a firstpresentation prohibition distance as a presentation prohibition distancefor the overtaking information; when the route traveling assist functionis not executed, a driver performs a manual steering of the vehicle anda navigation function of presenting the route and guiding to thepreliminarily set destination is executed, setting a second presentationprohibition distance shorter than the first presentation prohibitiondistance as the presentation prohibition distance; detecting a positionof the vehicle on the route; detecting whether or not there is atraveling direction change point on the route ahead of the position ofthe vehicle, the traveling direction change point being a point at whichthe vehicle is required to change its traveling direction; and when adistance from the vehicle to the traveling direction change point isshorter than the presentation prohibition distance, not performing thepresentation of the overtaking information.
 2. The travel control methodfor a vehicle according to claim 1, wherein the traveling directionchange point includes at least one of a branching point, a mergingpoint, an exit from a road, or a tollgate.
 3. A travel control methodfor a vehicle for presenting the vehicle traveling on a route to apreliminarily set destination with overtaking information as to whetheror not to accept execution of an overtaking assist function forovertaking a preceding vehicle by changing lanes through autonomoustravel control, the travel control method comprising: when a routetraveling assist function of controlling the vehicle to autonomouslytravel along the route is executed, setting a first presentationprohibition distance as a presentation prohibition distance for theovertaking information; when a navigation function of presenting theroute and guiding to the preliminarily set destination is executed,setting a second presentation prohibition distance shorter than thefirst presentation prohibition distance as the presentation prohibitiondistance; detecting a position of the vehicle on the route; anddetecting whether or not there is a traveling direction change point onthe route ahead of the position of the vehicle, the traveling directionchange point being a point at which the vehicle is required to changeits traveling direction, wherein when a distance from the vehicle to thetraveling direction change point is shorter than the presentationprohibition distance, the presentation of the overtaking information isnot performed, and when neither the navigation function nor the routetraveling assist function is executed, setting a third presentationprohibition distance shorter than the second presentation prohibitiondistance as the presentation prohibition distance.
 4. A travel controlapparatus for a vehicle, configured to: present overtaking informationas to whether or not to accept execution of an overtaking assistfunction for overtaking a preceding vehicle by changing lanes throughautonomous travel control of the vehicle traveling on a route to apreliminarily set destination; when a route traveling assist function ofcontrolling the vehicle to autonomously travel along the route isexecuted, set a first presentation prohibition distance as apresentation prohibition distance for the overtaking information; whenthe route traveling assist function is not executed, a driver performs amanual steering of the vehicle and a navigation function of presentingthe route and guiding to the preliminarily set destination is executed,set a second presentation prohibition distance shorter than the firstpresentation prohibition distance as the presentation prohibitiondistance; detect a position of the vehicle on the route; detect whetheror not there is a traveling direction change point on the route ahead ofthe position of the vehicle, the traveling direction change point beinga point at which the vehicle is required to change its travelingdirection; and when a distance from the vehicle to the travelingdirection change point is shorter than the presentation prohibitiondistance, not perform the presentation of the overtaking information.